The Tissue Bank Core C will provide the necessary mechanism to collect and distribute tissues from large numbers of patients to individual investigators. Because Ph negative MPD are relatively rare, individua investigators at a single institution cannot obtain tissues from sufficiently large numbers of patients to reach statistically valid conclusions within a reasonable time frame without Tissue Core C. Tissue Core C will provide tissues from large cohorts of patients at various stages of these disorders, as well as tissues from individual patients collected longitudinally during disease progression. Thus, the Tissue Bank Core C will be an invaluable tool to current and future studies on MPD. The specific aims of the Tissue Bank Core C are to: 1) Receive, process, and store tissues from MPD patients diagnosed at MPD Consortium clinical sites in an efficient and organized way. 2) Provide a central repository for MPD tissues that can be associated with basic data to be stored by Biostatistics and Data Management Core B. These data will include clinical laboratory data and familial demographics that will enable selection and distribution of tissues best suited for each translational research project. 3) Make the viably frozen tissues readily available to the MPD Consortium investigators for research studies. When available, tissues will also be available to the scientific community at large. 4) Perform biomarker assays, designed to predict disease progression and thrombotic complications, on MPD samples received at the time of diagnosis, and periodically during therapy. The functions of Tissue Bank Core C will be to: 1) acquire Ph negative MPD tissues, 2) act as a repository for the Ph negative MPD tissues, 3) distribute the MPD tissues research, and 4) perform biomarker analyses. Tissues collected will be available to members of the MPD Consortium and to the scientific community at large. Tissue Bank Core C will significantly facilitate translational research that will enhance diagnosis and staging of MPD and ultimately lead to the development of molecularly targeted therapies. PV and IM are disorders for which there are currently no effective treatments. PV and IM affect primarily patients >50 years of age and their annual incidences are estimated to be 2.8 and 0.4/100,000 people, respectively. The number of people over the age of 50 is increasing and therefore more people will be affected by these disorders in the future. Therefore, from a public health perspective it is imperative to develop effective therapies.